name	add-composite-signal-op
description	Add composite signal operators using existing primitives (no dedicated backend kernels needed)
source	auto-skill
extracted_at	2026-06-07T17:02:48.366Z

Adding Composite Signal Operators

When implementing signal operators that can be composed from existing Insight7 primitives (FFT, math, linalg), follow this streamlined workflow instead of writing dedicated backend kernels.

When to Use This Skill

Operator can be expressed as a combination of existing primitives (FFT, convolution, elementwise ops, etc.)
No sequential data dependency that requires a custom kernel
No performance-critical hot path that composite ops can't match

Examples: istft, sosfilt, upfirdn, channelize_poly, qmf, lombscargle

Step-by-Step Workflow

1. Add Declaration to Header

File: include/insight/ops/signal/<module>.h

/// @brief Brief description matching scipy.signal docs.
///
/// @param x Input array (1D, F32 or F64)
/// @param param Parameter description
/// @return Output array description
Array function_name(const Array &x, double param = 1.0);

2. Add Implementation to Source

File: src/ops/signal/<module>.cpp

Array function_name(const Array &x, double param) {
  INS_CHECK(x.defined(), "function_name: input is undefined");
  INS_CHECK(x.shape().ndim() == 1, "function_name: x must be 1D");

  Place cpu = CPUPlace();
  Place dev = x.place();
  DType dtype = x.dtype();

  // Move to CPU for computation (composite ops work best on CPU)
  Array x_cpu = x.to(cpu).to(DType::F64);

  // Compose using existing primitives
  // ... use fft::fft, mul, add, concat, etc.

  // Move back to original device
  Array result = /* ... */;
  if (dev.kind() != DeviceKind::CPU)
    result = result.to(dev);
  return result;
}

3. Add CPU Tests

File: tests/cpu/cpp/test_signal_<module>.cpp

TEST_F(Signal<Module>TestCPU, FunctionBasic) {
  std::vector<double> input = {1.0, 2.0, 3.0};
  Array x = to_array(input);

  Array result = signal::function_name(x, param);

  // Verify output shape
  EXPECT_EQ(result.numel(), expected_len);

  // Verify values
  const double *data = result.data<double>();
  EXPECT_NEAR(data[0], expected_val, 1e-10);
}

TEST_F(Signal<Module>TestCPU, FunctionInvalidInput) {
  Array bad = to_array(std::vector<double>{1, 2, 3});
  // Test error handling
  EXPECT_THROW(signal::function_name(bad, invalid_param), std::exception);
}

4. Add CUDA Tests

File: tests/cuda/cpp/test_signal_<module>.cpp

TEST_F(Signal<Module>TestGPU, FunctionBasic) {
  std::vector<double> input = {1.0, 2.0, 3.0};
  Array x = to_array(input).to(GPUPlace(0));

  Array result = signal::function_name(x, param);

  // Copy to CPU for verification
  Array result_cpu = result.to(CPUPlace());
  const double *data = result_cpu.data<double>();
  EXPECT_NEAR(data[0], expected_val, 1e-10);
}

5. Add Language Bindings

Python (bindings/python/insight_py.cpp):

sig.def("function_name", &signal::function_name, py::arg("x"), py::arg("param") = 1.0);

Python wrapper (bindings/python/insight/signal/<module>.py):

def function_name(x, param=1.0):
    """Brief docstring."""
    return _signal.function_name(x, param)

Python init.py: Add to imports and __all__.

Lua (bindings/lua/insight_lua.cpp):

sig["function_name"] = &ins::signal::function_name;
// OR for optional params:
sig["function_name"] = [](const ins::Array &x, sol::optional<double> param) {
  return ins::signal::function_name(x, param.value_or(1.0));
};

Lua wrapper (bindings/lua/insight/signal/<module>.lua):

M.function_name = _wrap({ "x", "param" }, function(x, param)
  return sig.function_name(x, param or 1.0)
end)

Julia C ABI (bindings/julia/insight_julia_capi.cpp):

Array *insight_jl_function_name(const Array *x, double param) {
  static thread_local Array result;
  result = signal::function_name(*x, param);
  return &result;
}

Julia wrapper (bindings/julia/src/modules/signal/<module>.jl):

function function_name(x::InsightArray, param::Float64 = 1.0)
    ptr = ccall((:insight_jl_function_name, LIB_INSIGHT), Ptr{Cvoid},
                (Ptr{Cvoid}, Float64), x, param)
    if ptr == C_NULL
        error("function_name failed")
    end
    return InsightArray(ptr)
end

Julia exports: Add to Insight.jl export list and const alias section.

6. Build and Test

cd build && make -j24
# Run new tests
./tests/insight_tests_cpu --gtest_filter="*<NewTests>*"
cd tests && ./insight_tests_cuda --gtest_filter="*<NewTests>*"
# Run full suite
./tests/insight_tests_cpu
./tests/insight_tests_cuda
# Pre-commit
cd .. && PATH="$HOME/.local/bin:$PATH" pre-commit run --all-files

Common Patterns

Sequential Filtering (sosfilt)

// Direct Form II transposed for each biquad section
for (int64_t s = 0; s < n_sections; ++s) {
  double w1 = 0, w2 = 0;
  for (int64_t i = 0; i < n; ++i) {
    double wi = y[i] - a1*w1 - a2*w2;
    temp[i] = b0*wi + b1*w1 + b2*w2;
    w2 = w1; w1 = wi;
  }
  y.swap(temp);
}

Overlap-Add Synthesis (istft)

// IFFT each frame, apply window, overlap-add
for (int64_t i = 0; i < n_frames; ++i) {
  Array col = extract_column(Zxx, i);
  Array segment = fft::ifft(col, nfft);
  segment = real(segment) * win;
  output[start:start+nperseg] += segment;
  norm[start:start+nperseg] += win * win;
}
output /= norm;  // Normalize

Polyphase Decomposition (channelize_poly)

// Reshape filter into [n_channels x n_taps], convolve each with input column
for (int64_t k = 0; k < n_channels; ++k) {
  std::vector<double> h_k = extract_polyphase(h, k, n_channels);
  std::vector<double> x_k = extract_column(x, k, n_channels);
  // Convolve h_k with x_k
}

Pitfalls

ndim() doesn't exist on Array: Use shape().ndim() instead
cast() doesn't exist: Use array.to(DType::F64) instead
Shape uses .dims()[i] not [i]: Access dimensions via shape().dims()
CPU computation: Composite ops work best on CPU; move data with .to(CPUPlace())
DType preservation: Convert to F64 for computation, convert back to original dtype at end
Device restoration: Move result back to original device if input was on GPU
Column-major vs row-major: Julia bindings use column-major; multi-dim arrays need care
std::vector as intermediate: Use std::vector<double> for CPU-only computations